This invention provides an improved method and apparatus for the hydrostatic testing of the integrity of a connection between two sections of pipe.
In the oil and gas industry, individual stands or lengths of pipe (drill pipe or casing pipe) are referred to by various terms, including joints, sections or segments. When these sections of pipe are joined together to form the pipe string that will be inserted into the well hole, it is necessary to test the connections between the various stands of pipe in order to determine if the connections will leak when subjected to the hydrostatic pressures that may be encountered in the drilling operation, pressures resulting from the introduction of drilling mud and other substances into the drilling operation, pressures from fluids and gases in the earth that may be encountered during the drilling operation, and, of course, the pressures of the crude oil or gas which hopefully ultimately will be brought to the surface through the pipe string. A fluid leak through a connection in the pipe string can have significant adverse effects on the drilling operation, from having to remove the pipe string from the well to replace the leaking connection (a time consuming and costly procedure) to loss of the well (which, of course, is an even more costly event). Over the years, there have been a number of methods utilized to test the connections between the various joints of pipe in the string before or contemporaneously with the string being inserted into the well hole to determine if the connection is likely to leak. The most commonly utilized method is some sort of hydrostatic testing procedure. This invention provides an improved method and apparatus for the hydrostatic testing of the connections between stands of pipe.
Heretofore, the hydrostatic testing of connections between joints of pipe utilized for the production of oil and gas has been generally accomplished by sealing off above and below the connection, either internally within the pipe body or externally on the pipe body, injecting hydrostatic test fluid, such as water, "slick water" (water with a surfactant added), gas or mixed gas, between these sealing elements of the testing apparatus and against the connection, and observing for a leak or pressure drop in the hydrostatic test fluid through the connection by use of a gauge or "sniffer" device (such as a mass spectrometer in the case of gas or mixed gas testing). More specifically, the connections to be tested usually are made up to a specified torque in order to create a specific bearing pressure between the sealing surfaces of the two sections of pipe being connected together. While most such testing is performed with the connection in the fully made-up position, that is, optimum torque is applied to the two joints of pipe, some hydrostatic test methods allow for testing of a connection in a partially made-up state. In any event, subsequent to the connection being made-up, either partially or to optimum torque, as indicated above, hydrostatic pressure is then applied to the connection, either internally or externally, as part of the testing procedure. We have discovered that errors can result in the testing process as a result of the fact that in almost all types of connections, the individuals who designed the sealing surfaces of the pipe have taken into account, and, in fact, are relying on the hydrostatic pressures likely to be encountered in the drilling operation to assist in securing the connection's seal. Most pipe joints are intentionally designed such that the hydrostatic pressures encountered by the connection during the drilling operation affect the bearing pressure (often also referred to in the industry as the contact pressure) between the sealing surfaces of the connection--thus "setting" or effecting the sealing characteristics of the connection. In fact, some connections are designed whereby a unit of hydrostatic pressure applied across the connection causes a multiple of that unit change in the bearing pressure of the sealing portion of the connection. Indeed, because of this design philosophy, most connections leak not when encountering maximum hydrostatic pressures in the drilling and completion operation and throughout the productive life of the well, but rather when encountering relatively low hydrostatic pressures. WE have discovered that because of this design philosophy, there is a likelihood the connection that will leak when subjected to relatively low hydrostatic pressures encountered during the drilling and completion operation and throughout the productive life of well will not be identified during the hydrostatic testing procedure. This is because in the prior art methods and apparatus for hydrostatically testing connections for leaks, the applied hydrostatic testing pressures themselves have the same effects as the designers contemplated for the hydrostatic pressures likely to be encountered during the drilling operations--the application of the pressures associated with the testing procedure itself "sets" or effects the sealing characteristics of the connection. We have discovered that depending upon the design of the sealing surfaces of the connection, the relative wall thickness of the mating sealing surfaces, and whether pressure is applied internally or externally, the bearing pressure between the connection's sealing surfaces may change significantly and thus obscure the fact that the connection is likely to leak when subjected to relatively low hydrostatic pressures encountered during the drilling and completion operation and throughout the productive life of the well. We have discovered that this change in the bearing pressure on the sealing surfaces of a connection as a result of the applied external or internal testing pressure is an important, perhaps even critical, factor in accurately determining the sealing capacity of most connections. There are, of course, certain types of joints, such as welded joints, in which if there is a leak in the connection, the leak path will be substantially perpendicular to the tubular pipe axis. In such cases, the locations and procedures for applying the test pressure to the connection is largely immaterial for purposes of the bearing pressure of the seal. However, the method and apparatus according to this invention is particularly useful in testing for leaks in a connection between casing or other types of tubing wherein the bearing pressure of the connection is sensitive to the pressure applied by the leak testing apparatus itself.
The improved method and apparatus for testing tubular connections according to this invention recognizes that the most accurate test method for predicting a connection's sealing capacity is that method which affects the connection's sealing surfaces bearing pressure the least per unit of applied pressure. The improved method and apparatus for testing tubular connections according to this invention applies pressure to specific surfaces of the connection in order to yield the least change in bearing pressure between the connection's sealing surfaces per unit of applied testing pressure.
We have also discovered there exists the very real possibility that a connection may be sensitive to varying load factors, such as tension or compression loads or loads introduced by temperature variations, that are common during the drilling and completion operations and during the productive life of the well, and/or have a cycle dependency such that the connection will leak upon subsequent pressure cycles. For example, the initial load cycle or pressure cycle may in some way introduce plastic strain into the connection and therefore reduce the connection's interference and bearing pressure of the sealing surfaces, or the connection's lubricant, sometimes referred to in the industry as pipe dope, may form an initial temporary seal during the initial pressure cycle but not hold during subsequent cycles since such a seal is not a reliable seal. The improved hydrostatic test method and apparatus according to this invention allows for the identification of these types of connections.
It is, therefore, an object of this invention to provide an improved method and apparatus for testing a connection between pipe joints in those situations in which the bearing pressure between the sealing surfaces of the connection is affected by the hydrostatic pressure of the testing fluid.
It is an additional object of this invention to provide an improved method and apparatus for testing a connection between pipe joints which is applicable for both internal and external testing and which applies pressure to specific surfaces of the connection in order to yield the least change in bearing pressure between the sealing surfaces of the connection per unit of applied testing pressure.
It is a further object of this invention to provide an improved method and apparatus for testing a connection between tubular members wherein the operator of the unit is provided the ability to selectively pulse or otherwise apply hydrostatic testing pressure in order to determine if the connection is sensitive to varying load factors or has a cycle dependency such that the connection may hold on the first initial pressure cycle but then leak on subsequent cycles.
It is a further object of this invention to provide an improved method and apparatus for testing a connection between tubular members wherein a plurality of pressure zones are established on the connection at locations designed to vary the bearing pressure between the sealing surfaces of the connection independent of the applied test pressure while observing for leaks before, during, and after varying the bearing pressure. The operator of the unit is provided the ability to selectively pulse or otherwise apply pressure in certain zones and observe pressure changes in other selected zones.
It is an object of this invention to provide an improved method and apparatus for testing a connection between pipe segments in which the bearing pressure of the connection is sensitive to the pressure applied by the leak testing apparatus itself and the operator is provided with data in a readily interpretable context in order to determine pressure anomalies.
Another specific object of this invention is to achieve the above objects with a visual graph or other display of the characteristics and results of the various parameters of the testing procedure.
Still another specific object is to achieve the above objects with computer-aided means for prescribing for a given connection the nature and extent of the pressure required at the specific locations to achieve or to substantially achieve accurate testing for the connection.
A further specific object is to meet the above objects with computer-aided means whereby digital data are available for control of automated apparatus to perform the testing method.
A further specific object is to achieve the above objects with a visual display of data which is recorded by a video cassette recorder or other means of permanent recordation for visual analysis later.
The invention itself, as well as additional objects and advantages thereof, will become apparent from the following description in connection with the accompanying drawings, in which like numerals represent like parts: